Gene duplication followed by functional and structural specialization is one of the primary forces of evolutionary change. Despite its importance in genome expansion, speciation and the generation of evolutionary diversity, such processes have been implicated in predisposition to human genetic disease by creating regions of sequence similarity capable of undergoing illegitimate recombination. Interestingly, an unusual functional property of the human genome has emerged in which large genomic segments have been predisposed to duplicate to the pericentromeric regions of chromosomes. The available data indicate that this process has occurred relatively recently (1-15 mya); that it involves the inter/ intrachromosomal transposition of genomic segments ranging from approximately 5-50kb in length and that it has contributed to considerable variation in the genomic architecture of these regions among the higher primates. The investigators hypothesize that this mechanism is an ongoing evolutionary process which results in considerable genomic variability and provides the molecular context for instability associated with these regions. The aim of this proposal is to 1) investigate the molecular mechanism responsible for such pericentromeric duplications and 2) to assess the impact of this process in contributing to heteromorphism of normal human chromosomes and chromosomes associated with pericentromeric instability. To this end, the proposal will focus on the comparative analysis of 670 kb of pericentromeric sequence from human cytogenetic band interval 16p11.1 which appears to have been the target of multiple pericentromeric duplication events. Combining large-scale comparative sequencing and FISH (fluorescent in situ hybridization) methods with other molecular biology techniques, this proposal will specially define the "domains" of paralogy within this 670kb interval, identify the sequence junctions for both the "ancestral" and duplicated loci, reconstruct the phylogeny of each duplication and address the impact of these events on normal and disease variation. Due to the recent nature of this phenomenon and a reference human genomic sequence, the results of this analysis provide a unique opportunity to investigate the molecular mechanism underlying this form of human genome evolution. In addition, these results should provide the framework for understanding the peculiar genomic architecture of pericentromeric regions of chromosomes and the involvement of this structure in creating genetic diversity as well as a proclivity to genomic instability associated with genetic disease.